wierd IP

I have two PC: A can B. both use win2k. and they use the same hub, and the hub connects to a cable modem. pc A connects to a printer, I'm trying to make the printer available to PC B too. and I found the following question:
A's IP: 66.31.**.***
B's IP: 24.128.**.***

how could A and B's IP so different while using the same hub? and the two PC can not ping each other using those IP.
Following network components are installed in both PC:
Internet Protocol(TCP/IP)
File and Printer Sharing for Microsoft Networks
Client for Microsoft Networks

Thanks for any help!

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